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José RepondArgonne National Laboratory
: Calorimetry reinvented
Colloquium at Georgia State UniversityAtlanta, GA
October 10, 2017
J.Repond: Calorimetry reinvented
2
Particle physics studies the nature of particles that are the constituents of what is usually referred to as matter (wikipedia)
These studies often involve the collision of stable particles (protons, electrons) at high energy, producing events with (more, many, new) particles
Examples of colliders: LHC, ILC, Tevatron, HERA, LEP, EIC…
Particle detectors detect the long-lived particles emanating from these collisions:
Charged: p, K±, π±, μ±, e±, Neutral: γ, n, KL0, ν
J.Repond: Calorimetry reinvented
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Particle Detectors contain a number of subsystems
- Vertex detector → measurement of tracks close to interaction point → measurement of secondary vertices (KS
0…)→ measurement of track impact parameters (charm, beauty)
- Inner tracking detector → measurement of charged tracks and their curvature (momentum) - Calorimeter → measurement of the energy of particles (destroys the particles) - Solenoid → provides magnetic field to bend tracks depending on their momentum - Muon chambers → identify tracks which punched through the calorimeter unharmed
…most colliding beam detectors look more or less like this one
destructive
4
Why do Jet Physics?
High energy particle colliders produce
Collimated jets of hadronic particles
Given an appropriate algorithm, particles in events can be associated to jets
parto
n
{p1, p2, … pn} → {J1, J2, … JN}
with n » N
Use jets to reconstruct momentum of partons study short distance QCD heavy particles decaying into qq, e.g. W±, Z0
Jets can be associated with partons ofunderlying hard scattering
5
2 Examples of measurements with jets
Dijet in photoproduction at HERA
→ reconstruction of the fraction of photon energy participating in the hard scattering
Dijet production in deep inelastic scattering at HERA
→ reconstruction of the fraction of the proton momentum taken by the interacting parton
e
jetT
jetTobs
yE
eEeEx
jetjet
2
22
11
)1(2
2
Q
Mx jjBj
J.Repond: Calorimetry reinvented
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Electromagnetic Showers IInitiated in matter by incident photons or electrons (positrons)
Dominant processes
Electrons → bremsstrahlung (emission of a photon, when subject to deflection from original trajectory)
Photons → pair production (creation of electron-positron pair in the
electric field of nuclei)
J.Repond: Calorimetry reinvented
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Electromagnetic Showers II
Interplay of bremsstrahlung and pair production
Leads to the development of a shower of particles
Sandwich calorimeter
Most widely used calorimeter concept in HEP Absorber plates interleaved with active sensors (e.g. scintillators) Absorber plates incite the particles to shower Active sensors measure particles through the ionization process
Particle Ab
so
rber
Act
ive
Shower in a calorimeter
Similar process for hadrons →hadronic showers
charqediparticle NE
J.Repond: Calorimetry reinvented
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EM and HAD Response in Calorimeters
Typical calorimetric response
To hadrons and electrons of same energy different
e.g. Evis(20 GeV e–)/Evis(20 GeV π–) ~ 1.6 in CDF
Hadronic showers in calorimeters
Have an electromagnetic and a hadronic component The fraction of these components fluctuate from shower to shower Plus, the response to em and hadronic component different (also within a single shower)
Poor resolution for hadronic showers
π- e-
ATLAS Forward calorimeter
J.Repond: Calorimetry reinvented
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Solution → Compensation
Equalize the response to e– and π– (of same energy) e/π ~ 1 Can be done with e.g. Uranium and scintillator sandwich calorimeters ZEUS: Thickness of scintillator tuned to provide e/π ~ 1
Hadronic jets of particles produced at colliders
Mixture of charged, neutral hadrons and photons How to optimize their energy resolution?
ZEUS
30 GeV electrons and pions
World’s best single hadron energy resolution for a colliding beam experiment
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Trend in Calorimetry
Tower geometry
Energy is integrated over large calorimeter volumes into single channels
Readout typically with high resolution (> 10 bits/channel)
Individual particles in a hadronic jet not resolved
ET
Imaging calorimetry
Large number of calorimeter readout channels (~107)
Option to minimize resolution on individual channels (1, 2… bits/channel)
Particles in a jet are measured individually
J.Repond: Calorimetry reinvented
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Advantages of Imaging CalorimetryParticle ID
Electrons, muons, hadrons → (almost) trivial
Software compensation
Typical calorimeters have e/h ≠ 1 Weighting of individual sub-showers possible → significant improvement in σE
had
Leakage corrections
Use longitudinal shower information to compensate for leakage → significant improvement in σE
had
Measure momentum of charged particles exiting calorimeter
Application of Particle Flow Algorithms (PFAs)
Use PFAs to reconstruct the energy of hadronic jets
J.Repond: Calorimetry reinvented
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Particle Flow AlgorithmsAttempt to measure the energy/momentum of each particle in a hadronic jet with the detector subsystem providing the best resolution
Particles in jets
Fraction of energy
Measured with Resolution [σ2]
Charged 65 % Tracker Negligible
Photons 25 % ECAL with 15%/√E 0.072 Ejet
Neutral Hadrons
10 % ECAL + HCAL with 50%/√E
0.162 Ejet
Confusion If goal is to achieve a resolution of 30%/√E →
≤ 0.242 Ejet
ECAL
HCAL
γ π+
KL
PANDORA PFA based on ILD detector concept
J.Repond: Calorimetry reinvented
Factor ~2 better jet energy resolution than previously achieved
18%/√E
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Application of PFAs
Past
Pioneered by ALEPH
Used by ZEUS, CDF…
Present
CMS
Future
ILC/CLIC detectors CMS endcaps ALICE forward Any new colliding beam detector
Detectors optimized for PFAs
J.Repond: Calorimetry reinvented
● Calorimeter needs to be optimized for photons: separation into ECAL + HCAL ● Calorimeters need to be placed inside the coil (to preserve resolution) ● To minimize the lateral size of showers, the RMolière of the ECAL needs to minimized ● The segmentation of the readout needs to be maximized ● The active layer or the depth of the E+HCAL needs to be minimized (cost) ● The front-end readout electronics needs to be embedded into the calorimeter
The role of the HCAL reduced to measure the part of showers from neutral hadrons leaking from the ECAL
Two performance measures of a calorimeter optimized for PFAs
J. Repond - Imaging Calorimeters
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Energy resolution for Identification of energy depositssingle neutral particles (minimize confusion)
PFA Implications for Calorimetry
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CollaborationGoal
Development and study of finely segmented/imaging calorimeters Initially focused on the ILC/CLIC needs Now widening to include the developments of all imaging calorimeter
Large prototypes built and tested to date
Silicon-W ECAL, Scintillator-W ECAL, Scintillator-Fe/W HCAL, RPC-Fe/W HCAL, RPC-Fe HCAL
4 continents
20 countries
60 institutes
364 physicists/engineers
2nd largest R&D collaboration in HEP
J.Repond: Calorimetry reinvented
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Electromagnetic CalorimetersRole
Precision measurement (position, energy) of photons
Absorber
Tungsten (alloy) -> small Molière radius = 3.5 mm Other possible absorbers not considered Depth about 20 X0, to minimize leakage into HCAL
Active media
Silicon pads (1 x 1 cm2 -> 0.25 x 0.25 cm2, 0.13 cm2) Scintillator strips with SiPM readout (45 x 10 mm2) MAPS (30 x 30 μm2 + digital readout) -> DECAL
Prototypes constructed and tested
CALICE Si-W ECAL (10k channels) SiD Si-W ECAL (10k channels) CALICE Scintillator-W (2k channels) ALICE FoCAL (39M channels)
J.Repond: Calorimetry reinvented
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How to test a calorimeter?
1) Linearity of the response
Ensures that
Important in traditional calorimeters Not so important in imaging calorimeters (as individual showers are being measured)
2) Resolution of the response to single particles
Typically fitted to
Constant term: non-uniformities, calibration…
Stochastic term: statistics, sampling…
Noise term: independent of energy
Don’t use
CEE
n
EE
CEE
E
)2/2/()( GeVNNEGeVNE visvis
J. Repond - Imaging Calorimetry
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Monte Carlo Simulations: GEANT4
Electromagnetic shower simulation
Reproduces results at the < 1 % level Multiple scattering still challenging Excellent tool to validate our understanding of the detector
Hadronic shower simulation
Greatly improved in the last few years Precision better than 10% (shapes < 20%) Choice of different models combined into various Physics lists
Adequate simulations are aprerequisite for understanding
the physics of a new technology
Linear within ±1% up to 45 GeV Resolution adequate
-> Negligible contribution to σ(Ejet) Excellent agreement with GEANT4 simulation
19
CALICE Silicon-Tungsten ECAL
Both concept and technical implementation validated
%1.01.1)(
1.06.16
GeVEEE
Linear within ±1% up to 32 GeVResolution quite good
-> Negligible contribution to σ(Ejet)Excellent agreement with simulation
20
CALICE Scintillator-Tungsten ECAL
Both concept and technical implementation validated
%1.1)(
4.06.12 6.07.0
GeVEE
E
21
ALICE Forward Calorimeter Upgrade
The ultimate digital calorimeter
Pixels of 30 x 30 μm2 area Total of 39 million channels 1-bit readout -> digital Energy reconstructed as function of number of hits
Granularity particularly important in forward direction
244 GeV electronLayer 4 Layer 8 Layer 12
Response surprisingly linear up to 244 GeV
Resolution not overwhelming
%23)(
430
)(
6
GeVEGeVEEE
22
Hadronic CalorimetersRole
Measurement of neutral hadrons (n, KL0)
Absorber
Steel preferred Tungsten was also explored More compact calorimeter (reduces cost) Degraded resolution (absorption of em component)
Active media
Scintillator pads (3 x 3 cm2) Resistive Plate Chambers (1 x 1 cm2) GEMs, Micromegas (1 x 1 cm2)
Readout
Scintillator -> 14-bit = analog Gaseous -> 1-bit = digital
Large prototypes constructed and tested
CALICE AHCAL(8k channels) CALICE DHCAL (500k channels) CALICE SDHCAL (400k channels)
23
Pions between 8 and 80 GeV/c
Software compensation
Based on energy density weights Improves both linearity and resolution
CALICE Scintillator-Steel HCAL
Both concept and technical implementation validated
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CALICE RPC-Steel HCAL – the DHCALEnergy reconstruction
To first order E proportional Nhit Response saturates (due to finite pad size) Response fitted to a power law Nhit = aEb+c Energy reconstructed as
-> Linear response within ±2%
Energy resolution
Not as good as the AHCAL Levels out at high energies (not a concern!) Can be improved with software compensation techniques
Offers an order of magnitude more granularity than AHCAL
Both concept and technical implementation validated
b hitrec a
cNE
%1.03.10)(
1.04.51
GeVEEE
J. Repond - Imaging Calorimeters
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Timing measurements
Measurement of shower timings using
Scintillator pads or RPC with pads
Positioned downstream of
Steel stack or Tungsten stack
Comparison with hadron shower models
Average 60 GeV shower in 4D
Use reconstructed interaction point in AHCAL/DHCAL
The power of imaging calorimeters
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Electron-Ion Collider EICPolarized ep, eA collider
√s = 35 – 180 GeV Luminosity = 1034 cm-2s-1
Two possible sites
Brookhaven -> eRHIC Jefferson lab -> JLEIC
Scientific goals
Study of perturbative & non-perturbative QCD Tomography (including transverse dimension) of the nucleon, nuclei Understanding the nucleon spin Discovery of gluon saturation… Construction to start in 2025
Community optimistic about prospect of realization
J. Repond - Imaging Calorimetry
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Quantum Chromodynamics QCD
Theory of hadronic interactions (no doubts!)
Has been validated in countless experiments (LEP, HERA, Tevatron, LHC…) where perturbative calculations are possible (high energy -> small coupling)
A deeper understanding of QCD requires exploring
The non-perturbative regime of the theory
3D tomography of the nucleon and nuclei
Generalized Parton Distributions (GPDs) Transverse Momentum Distributions (TMDs)
Contributions to the nucleonic spin Confinement Nuclear modifications of the parton density functions Non-linear evolution (saturation) ….
These are currently all open questions
J. Repond - Imaging Calorimetry
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Measurements at the EICPhysical quantity Process Measurement
challenges
Structure functions F2, FL
Nuclear structure functionsInclusive scattering Electron identification,
background rejection, luminosity
Spin structure functions Inclusive scattering + polarization
Gluon density Charm,dijet production…
Secondary vertex, pion/kaon separation, hadronic jets
Generalized PartonDistributions GPDs
Deeply VirtualCompton Scattering
Forward proton,background rejection
Transverse MomentumDistributions TMDs
Semi-inclusive DeepInelastic Scattering
Pion/kaon separation
Nuclear PDFs Scattering on nuclei Nuclear fragments
Many more
J. Repond - Imaging Calorimetry29
Requirements for EIC Detectors
Vertexing
Event vertex, secondary vertices, track impact parameter
Electron identification and measurement
-4 < η < 4
Hadronic jet measurement
Excellent energy resolution (kinematic reconstruction)
Pion/kaon/proton separation
For most of the solid angle identification needed for p < 7 GeV/c In forward direction needed for p < 50 GeV/c
Forward proton
Large acceptance for momenta up to almost beam energy
Forward neutron
Excellent energy and angle measurement
Vertex detector
Central tracker
Calorimeter
TOF or Cerenkov
Roman pots
00 calorimeter
PolarimeterLuminosity measurement
J. Repond - Imaging Calorimetry
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4 Detector Concepts for the EIC
Jefferson lab concept
sPhenix -> ePhenix Argonne concept: SiEIC
Brookhaven concept: BEASTPHENIX#Y>#ePHENIX#Path#
4#4#
By ~2025
By ~2020
ePHENIX
PHENIX sPHENIX
Evolve sPHENIX (pp and HI detector) to ePHENIX (DIS detector)
! To utilize e and p (A) beams at eRHIC with e-energy up to 15 GeV and p(A)-energy up to 250 GeV (100 GeV/n)
! e, p, He3 polarized
! Stage-1 luminosity ~1033 cm-2 s-1 (~1fb-1 /month)
J. Repond - Imaging Calorimetry
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The SiEIC Concept
Optimized for Particle Flow Algorithms (PFAs)
Measure each particle individually with the system providing the best E/p resolution
Based on the SiD concept
Originally developed for the ILC High precision silicon tracker (5 vertex + 5 outer layers) Calorimeters with extremely fine segmentation (Silicon, RPCs)
In general
Hermetic enclosure of interaction region Concept not yet optimized for the EIC environment Reduced magnetic field (5 –> 2.5 T) Reduced depths of calorimeters Longer barrel (increased forward detection)
Optimal detector means maximum use of luminosity
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The 5D Concept
Particle identification ( π – K – proton separation)
Important at the Electron-Ion Collider (EIC) Particle momenta < 10 GeV/c for most of the solid angle Time – of – flight with 10 ps resolution would do the job
The 5D concept
Measure (E,x,y,z,t) for every hit in tracker + calorimeter Requires ultra-fast silicon sensors Eliminates the need for additional PID detectors for most of the solid angle
Ultra-fast Silicon Sensors
Currently being developed based on the LGAD technology Best timing resolution about 27 ps Further improvements ongoing Interest in developing ultra-fast CMOS sensors (addition of amplification layer)
arXiv:1608:08681
Event generation
Produce the simulation input events
Detector simulation
Particle transport through detectors
Digitization
Turn energy deposits in active media into detector hits
Reconstruction of
Event vertex, charged tracks, Particle Flow Objects (PFO)
Perform analysis
Collection of benchmark analyses
33
Full simulation and reconstruction chain
Tools
HepSim
GEANT4 DD4Hep
LCSim
LCSim
Root scripts
Dat
a M
od
el
34
Simulation Studies
Single Particle Resolutions
Generated photons with 1 – 30 GeV Spread over most of solid angle
Determination of TOF Requirement
Using timing information in tracker and ECAL For each track fit time versus path length
Photon energy resolution
TOF PID using silicon with 10 ps resolution
Reconstruction of the F2 Structure Function
Use MSTW PDF to generate DIS events Use CTEQ PDF to correct for acceptance (problem with CTEQ phase space) Validation of entire simulation too chain
Comparison of true and reconstructed F2
35
Electron Method
Results
works quite well in general -> In particular for Q2
and at low-x
Poor resolution
at large-x or small-y (here other methods are better)
J.Repond: Calorimetry reinvented
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Conclusions
Trend towards imaging calorimeters for future applications
leading the development of such devices
Various technologies for imaging calorimetry have been validated Further R&D remains to be done
3/4 LHC experiments have adopted or are considering adopting CALICE technologies for their calorimeter upgrades
Argonne is developing a concept of a multipurpose 5D detector for the EIC
J.Repond: Calorimetry reinvented37
Backup Slides
J.Repond: Calorimetry reinvented
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Calorimetry for HEP Colliders at Argonne
HRS (PEP)ZEUS (HERA)
ATLAS (LHC)
DHCAL (ILC/CLIC)